Field of the Invention
The present invention relates to the field of transmitting or receiving antennas as radiating elements that can reach significant directivity levels at frequencies in the vicinity of one or several GHz.
The invention also relates to a one- or two-dimensional array antenna with a permanent or reconfigurable beam formation including a plurality of basic antennas according to the invention positioned on a surface.
Basic antennas of the EBG (Electromagnetic Band Gap) type, each having a structure designed on the principle of Electromagnetic Band Materials and each having a radiation diagram capable of forming a spot close to a disc on a lighted surface, are traditionally used as radiating elements of a more complex antenna.
Description of the Related Art
International patent application WO 01/37373 describes several embodiments of this type of basic antenna. According to this document, a basic antenna of the EBG type traditionally comprises a probe capable of converting electricity into electromagnetic energy and vice versa, and an assembly of elements made from at least two materials differing by their permittivity and/or their permeability and/or their conductivity within which the probe is positioned. This assembly traditionally includes a structure designed based on the principle of Electromagnetic Band Gap (EBG) materials. This structuring makes it possible to improve the directivity of the basic antenna, by ensuring the radiation of the basic antenna as well as spatial and frequency filtering of the electromagnetic waves produced or received by the basic antenna.
However, when they are assembled and juxtaposed in an array antenna, the basic antennas of the EBG type have significant coupling. This strong coupling creates harmful and disruptive interactions between the basic antennas, due to the capture and uncontrolled redistribution by each probe of the energy emitted by the neighboring probes. This results in radiation diagrams of the corresponding array antenna that are generally chaotic and not very directive. Furthermore, the basic radiating surfaces generated by each source are superimposed on one another and form a non-uniform surface that is not very acceptable for agility.
The invention aims to propose a basic antenna of the EBG type with high directivity capable of generating a radiating surface with a predefined shape whereof the coupling with the neighboring antenna of the same type is improved, i.e., a basic antenna that disrupts and is disrupted little by surrounding basic antennas with an identical structure, and the generated radiating surface of which is quite limited, thereby avoiding overlapping of the radiating surfaces with each other.
To that end, the invention relates to a basic antenna designed to form an element of an array antenna comprising:                a probe capable of converting electricity into electromagnetic energy and vice versa;        a planar electromagnetic wave reflector bearing the probe; and        an assembly of elements made from at least two materials differing by their permittivity and/or their permeability and/or their conductivity, the assembly including:                    a structure configured based on the principle of Electromagnetic Band Gap materials and having a periodicity in the direction orthogonal to the planar reflector; and            a cavity in contact with the planar reflector and the structure;the probe being contained in the plane of the reflector in contact with the cavity or in the cavity in contact with the planar reflector, the cavity constituting a defect in the periodicity of the structure giving the assembly the behavior of an Electromagnetic Band Gap material with a defect, in which the positioning of the elements in said assembly ensures the radiation and a spatial and frequency filtering of the electromagnetic waves produced or received by the probe, said filtering in particular allowing one or more operating frequencies of the basic antenna inside a frequency band gap;                        
said basic antenna being characterized in that it comprises a wall enclosure capable of reflecting the electromagnetic waves at the operating frequency or frequencies, said wall enclosure being an extension in the direction orthogonal to the planar reflector and simultaneously surrounding only the probe, the cavity and the structure, making it possible to generate a basic radiating surface with a predetermined shape and imposed by the wall enclosure.
On the upper surface of the device, this wall enclosure creates a radiating surface with a shape predefined by its contour, while the traditional EBG basic antennas with no wall enclosure generate radiating surfaces with a circular geometry larger than the physical opening.
According to other features considered alone or in combination:                the wall enclosure has a transverse section whereof the inner contour is fitted in a circle and whereof the ratio of the surface area contained in the circle to the surface area contained in the inner contour is comprised between 1 and 5;        the wall enclosure has a transverse section whereof the outer contour is a regular polygon preferably having three or four sides;        the wall enclosure has a transverse section whereof the outer contour is a first regular polygon and whereof the inner contour is a second regular polygon, the second polygon being homothetic with the first polygon, the first and second polygons being concentric and preferably having three or four sides;        the probe is comprised in the set made up of strip antennas, dipoles, circular polarization antennas, slots and coplanar wire-plate antennas; and        the probe is a strip antenna, and the wall enclosure includes four metal walls that delimit a rhomb having a height along the axis orthogonal to the planar reflector and a transverse section relative to that same axis with a square shape, the height, length, respectively, of one side of the square being substantially equal to one time, respectively half of, the/the wavelength associated with the operating frequency of the basic antenna.        
The invention also relates to a one- or two-dimensional array antenna including a plurality of joined basic antennas, defined above and arranged relative to one another to compactly cover, in a single piece, one or more planar support surfaces, thereby generating pixelated radiating surfaces responsible for several radiation lobes. A radiating surface is therefore generated, on which electromagnetic fields are responsible for the desired radiation under the principle of radiating equivalence of a radiating opening, known by those skilled in the art.
According to other features considered alone or in combination:                the total number of basic antennas making up the plurality is equal to a number of rows N multiplied by a number of columns M, and the basic antennas are arranged relative to one another to compactly cover a rectangle of a planar support surface so as to form a rectangular matrix of N·M basic antennas with N rows and M columns, and the wall enclosures across from any two neighboring basic antennas are in contact;        the one- or two-dimensional array antenna further includes:                    power distributing means;            supply means for the plurality of basic antennas in amplitude and phase, said supply means being connected at their input to the power distributing means, and connected at their output to said plurality of basic antennas by switches that can be controlled to selectively power or extinguish each basic antenna; and            the power supply means include phase shift means and/or amplification means.                        